Increasing



1949 I G. w. FILES Re. 23,179

ROENTGENOLOGICAL METHOD AND APPARATUS Original Filed June 28. 1946 gIIIII/IIIIIIIIIIIIIIIIIIIII"HIHHIUIIHIHIIIIllllIllllllllllllllllllllllfllll\mlI\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\'2] I 9J9 1 :sfl

2 2 E k 2 U.) D! E LL 5 d1 3 .Q r- 2 5 NO GRID a A N {737 297:1. o:(150/? 51 es, execairajaflgoffimw dz; deceasm INCRE-EASINGP RAY m'remsrrw mW WgM Reissued Dec. 6, 1949 UNITED STATES PATENT OFFICEROENTGENOLOGICAL METHOD AND APPARATUS New York Original No. 2,435,823,dated February 10, 1948, Serial No. 679,940, June 28, 1946. Applicationfor reissue January 15, 1949, Serial No. 71,142

Matter enclosed in heavy brackets I: appears in the original patent butforms no part of this reissue Specification; matter printed in italicsindicates the additions. made by reissue 10 Claims.

The present invention relates in general to roentgenology, and has moreparticular reference to apparatus for, and methods of, making improvedshadOW pictures, on ray sensitive material.

Ray pictures, of course, are made by exposing an object to be picturedto the action of radio active emanations, from a suitable source, and byapplying the resulting ray shadows of the ob.- ject to a layer of raysensitive material, either in the form of sensitive film or sensitivefluorescent screen means. Perhaps the most important defect apparent inshadow pictures is the indefinite, blurred character of ray picturesmade in accordance with existing picture making techniques, the value ofray pictures, in the final analysis, being the clarity and exactnesswith which they present the true internal strucs ture of tissues ormaterial being pictured.

Many variable factors, of course, are necessarily dealt with in themaking of shadow pictures, including the intensity of the activating raybeam, which, where the activating beam comprises X-rays produced by asuitable generator, depends upon the electrical characteristics andcontrol of the generator; the nature of the tissues being pictured,including tissue structure, as well as sectional thickness; thecharacteristics of the ray sensitive picture receiving layer; thecontrol of secondary radiation, that is to say, radiation other thanthat from the ray source, such as may be generated in the material ortissues being pictured as a result of exposure to the primary activatingray; and other variables, including time of exposure of the tissuesbeing pictured to the activating ray, as well as the judgment of thepicture making technician Ever since the establishment of roentgenology,as an art, scientists and others have been striving to improve thecharacter of shadow pictures by improving the definition, or clarity, ofthe ray picture. In this connection, every variable aspect which entersinto the making of ray pictures has been carefully and criticallyexamined in an effort to improve picture definition, or quality.

Accordingly, an important object of the present invention is to providefor the production of shadow pictures having fine definition or detailsharpness characteristics, to thereby produce pictures having superiorvalue for diagnostic and other purposes.

Much effort has been expended upon the production of sensitive materialfor receiving shadow pictures, in an effort to produce material highlysensitive to slight variations in the intensity of rays impingingthereon. In this connection, sensitive material, of necessity, must showappreciable contrast characteristics in order to distinguish betweenrays passing through tissues of unlike opacity. At the-same time, ma-

terial having good contrast characteristics for the sake of shadowperception in the resulting picture will tend to impair definition, thatis to say, the ability to distinguishbetween the shadows of rays passingthrough tissues having slightly different ray transmittingcharacteristics.

Accordingly, another important object of the invention is to provide forthe production of ray pictures of superior quality, as to definition,

Without sacrifice of contrast factors to any deleterious extent.

Another important object is to improve definition in ray pictures byproviding for the substantial, if not complete, elimination of theeffects of secondary radiation; a further object being to eradicate thedeleterious effects of secondary radiation in the making of raypictures.

Another important object is to provide improved means for eliminatingthe effects of secondary radiation, in ray picture making; a furtherobject being to provide improved diaphragm structures for theelimination of secondary ray efi'ects.

Another important object is to provide improved operational techniquesto utilize the improved diaphragms of the present invention to Figs. 3,4, and 5 are enlarged views of portions of the diaphragm shown in Fig.2;

Fig. 6 is a fragmentary view of a portion of the diaphragm on a greatlyenlarged scale; and

Fig. 7 shows comparative diaphragm performance graphs.

It should be understood that roentgenologic pictures are made, asindicated in Fig. l, by exposing an object H, to be pictured, toradioactive rays l2 emanating from a suitableray-source l3, such as theanode It of an X-ray generator l5, energized for the production ofX-rays, at said anode, by electrons emitted by-"the-cathode l6 of thegenerator, and impelled to, impinge upon the anode under the influenceof electrical potential applied between the anode and cathode. A shadowpicture of the object H, soactivated' by the rays l2, may be formedupona layer'of: ray sensitive material ll, disposed adjacent the object, in position to receive a shadow, picturetherm of upon the layer ll.In this connection, the layer may comprise; any suitable: ray sensitivefilm for the making offa permanentpicturaor it: may comprise a suitableray sensitive fluorescent screen.

Definition in the resulting my picture isaffected, to some extent, bythe intensity: of the: activating rays, in accordance with the'nature ofthe material being pictured; Rays oflow intensity, in passing readilythrough relatively ray anations of relatively highintensity capable of"penetrating andpi'cturing fairly impermeable, or solid, material,maytend to wash out or destroy the picture definitionof highly permeabletissues. Consequently, ray intensity, in making shadow pictures inaccordance with current practice, has. to be carefully and accuratelydetermined; in accordance with'the'nature of the tissue to bepi'ctured'; and it is often impossible to picture rel--ativelypermeable, and impermeable or opaque, material simultaneouslywith any degree of satisfactory definition in the'various pictured partsof 'substantiall'yunlike' opacity.

Where X-rays, produced by a suitable genera-= tor, are employed inshadow picture making, the ray intensity-may be determined, in part, bythe rate of electron emission from the electron-emit ting cathode of thegenerator; The emitting element is usually a filament, electronemissionfrom' whichis controlled by regulating the elec-' trical currentdelivered to the filament for the purpose of' exciting the same forelectron emission. Ray intensity, however, is, also, a funo-- tion ofthe rate and velocity of impact of electrons upon the anodetargetof thegenerator, the same, in turn, being a function of uni-directionalelectrical power applied between the an ode and cathode of the generatorfor i'mpelling electrons, emitted at the cathode, to impinge upon theanode. As a consequence, the valueof filament excitingjcurrent,.as wellas anode-cathode potential and current; in the generator, are importantfactors ultimately ailecting the character of ray pictures produced withthe-generator functioning as a ray source. Ordinarily, however, it ismore. convenient to adjust anode-cathode power than filament current, soan X-ray generator is usually arranged to operate at constant filamentcurrent, ray intensity being adjusted by altering either. anodepotential or current, or both. 1

.rent andv exposure time interval.

Duration of exposure is, also, a factor controlling definition in theresulting radiographic picture, being related in this respect to rayintensity. By increasing or decreasing the exposure interval in pictureproduction at a constant ray intensity optimum, exposureinter-vals maybe determined, empirically, for each tissue type, and thickness, and forevery kind of sensitive material used in the making of shadow pictures.It is. generally true. that increasing exposure time will improvedefinition in pictures of relatively dense tissue structures, but willtend to wash out and obliterate, or fog; picture portions of tissuerelatively transparent to the activating rays. In this connection-also,it is usual to measure ray intensity, in radiography, as energy applieddur-- ing-the exposure or picture making interval. This dataconveniently may be expressed as a function of the-multiple of anodevoltage, anode cur- Since unidirectional power is usually suppliedthrough suitable rectifiers from an alternating current power source,and since: it. is more convenient; to:

measure the power drawn from the source than to measure it at the pointof delivery in the genkilovolts of potential (k'. v. p.)-and'milliarnperes.

of current,. drawn from the power source. Furthermore, since it is moreconvenient to adjust current and time of. exposure than. to, varyvoltage, it is usual to alter ray intensity by varyingmilliampere-seconds (In; a. s.), either by changing the anode current.supplied to the generator during an exposure interval, orby changingthe;

duration" of the exposure interval;

Since radioactive: emanations, or rays, passse lectivelythroughmatterof, different, kinds, and? since? the intensity of a ray decreasesproportion'ally as it passes through matter, each dif-- ferent kind ofmatter decreasing ray intensity in accordance with its individual raytransmittingcharacteristics,. the character ofaray picture of 'anyobject will be affected'bythe nature of the tissue, or tissues,composing the object, including the tissue: thicknesses through whichthe pass.- Asa consequence, the definition and clarity of a shadowpicture of a relatively thick body made with relatively low intensityrays may be considerably'less than definition accomplished in,

picturing a relatively thinner body of the same type of matter; and thedifierence can not necessarily be reduced merely by increasing theintensity ofrays utilized in picturing the relatively thicker body.Increasing ray intensity, as here,- tofore mentioned, may-result merelyin washing out the definition in. the picture portion corresponding withrelatively more ray permeable portions of the'object being pictured.

During the development of the radiographic art, technicians, by trialanderrormethods, have:

tion by Gustav Bucky of the fact that the object being pictured, whenexposed to picture making ray emanations, itself may become energized asa ray source, substantially throughout, thereby constituting the variousportions of the object being pictured as secondary sources of rayemanations, as indicated at ill in Fig. 1, such ray emanations,impinging on the sensitive picture receiving material, fromsubstantially every direction, being responsible for fogging, blurring,and consequent lack of detail definition in the resulting picture.

Bucky announced his discovery and hi method of controlling so-calledsecondary radiation, in the year 1913, and provided a multiple celldiaphragm, or grid. located between the object being pictured and thelayer of sensitive picturereceiving material, in an effort to suppressthe effects of secondary radiation,

Crude as the original Bucky device was, it demonstrated that secondaryor scattered radiation from the object being pictured constitutes thegreatest single detriment to detail visibility, or definition, in raypictures.

In spite of the Bucky discovery, the characteristics sensitive picturereceiving material have received far more attention, both from thestandapoint of improving the sensitive material and technique of usingthe same, as well as the improvement of auxiliary apparatus, includingray generators.

So far as definition in the resulting picture is concerned, it isdesirable that the activating rays emanate from as small a spot aspossible in the generator. Even in the early days of roentgenography,X-ray generators having exceedingly fine focal spots were available.X-ray tubes presently available have no finer focal spots than earlygenerators. It is true that the recently developed rotating anodegenerators provide a means for using exceedingl fine focal spots atsufficiently high energy, or X-ray, intensity to obviate loss of detaildue to unpreventable motion of the part being pictured. The rotatinganode tube, however, except for adding certain facilities in operativeprocedure, has done nothing to improve detail visibility, other thanobviating blurring in the resulting picture due to motion of the partbeing pictured.

One of the defects of the original Bucky diaphragm lies in the fact thatits grid pattern is pictured as a shadow on the sensitive material, beit film or fluoroscopic screen, such pattern detracting, to aconsiderable extent, from the clarity of the picture, and therebyminimizing the improvement in definition brought about through thereduction of secondary fog by use of the diaphragm.

The Bucky diaphragm, however, was improved by Hollis Potter, in the year1916, who proposed the elimination of the diaphragm grid shadow from theresulting picture by maintaining the diaphragm in carefully calculatedconstant motion, whereby to blur to extinction the shadow picture of thegrid without, however, affecting the shadowgraph of the object beingpictured.

Under the impetus of the Potter discoveries, the Bucky diaphragm hasevolved into a structure comprising alternate strips of ray imperviousmaterial, such as lead, and ray pervious spacing strips of material suchas wood, theUnited States patent to Wantz and Kizaur, No. 2,115,755,showing a recently developed form of the Potter- Bucky diaphragm.

A grid IQ for controlling secondary radiation, such as may emanate frompoints I8 in the body II, is shown in Fig. 1 of the drawings submittedherewith.

It should be understood that the ray impervious strips in a Potter-Buckydiaphragm are substantially equally spaced apart by means of interveningstrips of ray pervious material. These impervious strips commonly are ofthe order of /50 inch in thickness, having a width of the order of inch,with a spacement between adjacent ray impervious strips of the order of/6 inch. The grid ratio, that is to say, the ration of strip depth tostrip spacement, is of the order of 4. The filter factor, that is tosay, the ratio of the spacement between impervious strips to thethickness of the impervious strips, is of the order of 8.

An inherent disadvantage of the Potter-Bucky type diaphragm is that, inexcluding secondary radiation from the sensitive film or picturereceiving screen, it also excludes a portion of desirable picture makingray emanations, and to that extent impairs the possible optimum qualityof the resulting picture. The filter factor is a measure of thisdisadvantage which requires increased energy, or ray intensity, with.corresponding difficulties, in the making of shadow pictures throughPotter-Bucky type diaphragms. Increasing the filter factor, to minimizethis disadvantage, as by decreasing strip width, is, of course, limitedby mechanical considerations. Increasing the factor, by increasing stripspacement, reduces the grid ratio and impairs the beneficial effects ofthe diaphragm. A factor of 8, however, is practicable and does not verymaterially increase the ray energy required for the making of pictures.

There has been very little alteration in the structure, arrangement anduse of the Bucky type diaphragm since the Potter suggestedmodifications. During the last thirty years Potter- Bucky typediaphragms, of grid ratios ranging between 4 and 8, have been made andused, and grids having a ratio of 6 have been accepted as the ultimatepractical diaphragm so far as definition in the resulting picture isconcerned. Perhaps the most informative research, in this connection,since the work of Potter, was the work of R. B. Wilsey, who reported theresults of his investigations during the year 1921. In the course of ageneral study of the scattering of X-rays under the conditions of deeptissue roentgenography, as through water layers varying in depth up to10 inches, Wilsey found that scattered radiation affecting the film wasfrom 2 to 11 times as intense as the primary ray beam. The relativeintensity of scattered to primary radiation was little affected by theintensity of the primary ray beam measured in terms of the voltage ofthe tube comprising the X-ray source. Wilsey also found that scatteredor secondary radiation is little affected by the use of filters betweenthe material being pictured and the sensitive picture receivingmaterial, nor by the use of intensifying screens in conjunction with thefilm receiving material.

' Wilsey reported, further, his opinion that the only effective meansfor reducing the effects of scattered radiation lie in the use of theBucky diaphragm principle.

The present invention was made after careusing diaphragms for thepurpose of increasing detail sharpness in ray pictures.

A phenomenon noted in connection with the employment of the Buckydiaphragm in conventional fashion is the effect commonly referred to asunder cutting. Under cutting results in the apparent washing out of themarginal portions in the shadow picture of a relatively ray opaqueobject being pictured, and is, no doubt, present in pictures madewithout employing a diaphragm. Insuch pictures, however, under cuttingis not readily apparent, for the reason that secondary rays scattered inevery direction will completely under cut the image of a relativelyopaque object, so that its image in the final picture, beingsubstantially entirely under cut, does not show any appreciable undercutting at all. With the advent of the Potter-Buckydiaphragmimprovement, under cutting became more apparent in the edge portions ofshadow pictures of relatively opaque objects, but the effect wasaccepted as caused by diffraction of rays at the edges of the relativelyopaque object being pictured, the notion that such under cutting mightbe caused by such secondary radiation as might pass through thediaphragm being discounted, for the reason that the phenomenon occurseven where a piece of X-ray impervious material, like lead, is picturedwith no surrounding matter to afford a source of secondary radiation. Inany event, during the past thirty years, in no instance has anyreference been made to the removal of secondary radiation for thepurpose of eliminating under cutting.

It had, also, been noted that increasing ray intensity, when usingPotter-Bucky diaphragms,

did not affect under cutting, and that employment of ray intensitiesabove critical values resuited in an actual diminution of tissuedifferen tiation in the resulting picture.

Potter had shown that a grid having a ratio of 2% absorbs 76% ofsecondary radiation, that a ratio 4 grid absorbs 83%, that a ratio 5grid absorbs 86%, while a ratio 6 grid absorbs 89% of secondaryradiation, and that a ratio 8 grid would absorb substantially allscattered radia-- tion.

Wilsey, as a result of his exhaustive studies, had recommended, foroptimum results, grids having a ratio of 5.

It was an accepted principle that grids having ratios of the order of 6to 8 aiford the ultimate in beneficial grid construction so far as thesuppression of the definition destroying effects of secondary radiationare concerned. There is noindication whatsoever in available literaturethat anyone, prior to the present invention, gave any thought toimproving the general diagnostic ray picture technique through a changein Bucky diaphragm construction. In fact, considerable information isavailable, in addition to that given herein, tending to indicate thatgrid ratios in excess of 8 are of no value whatever, tending merely tocomplicate the manufacturing and operational picture.

The present invention, thus, was conceived by discounting the apparentteachings of earlier authorities on the subject. The inventor perceivedthe possibility of providing and using diaphragms for the elimination ofsecondary radiation along lines hitherto considered contrary to theteachings and experience of prior investigators. Accordingly, theinventor prepared diaphragms having various grid ratios, as follows:

Strip Width Grid Ratio Strip Strip Diaph Thickness Spacement Mils MilsMils NNMMNI A filter factor, or ratio of strip spacement to stripthickness, of 8 was maintained in all of the above grids.

As shown in Figs. 2-5, these grids consisted of alternate strips ofexceedingly thin lead foil 20 and thin wood spacing strips 2i, thestrips being angulated to arrange the foil strips in planes radiatingfrom a focal point disposed 40 inches from, and on a line extending atright angle with respect to, the plane of the diaphragm at its midpoint, Fig. 6 showing, to exceedingly large scale, substantially theexact relative proportions of the strip sections, in the mid portions ofthe ratio 8 grid. The other higher ratio grids emplayed the sameexceedingly small strip thick-- nesses and spacements, but varied as tostrip width, in order to vary the grid ratios of the variou diaphragmunits.

After completion, the foregoing grids were tested and used to accuratelydetermine their relative operating characteristics. In this connection,it has been recognized for a number of years that more consistentradiographic results are obtainable by using relatively high k. v. p.values for the operation of the X-ray generator, the higher the k. v. p.value, generally speaking, the higher the intensity of the resulting raybeam. The foregoing is particularly true of the so-called modern type ofX-ray film. Film with modern characteristics has been in use forapproximately 8 years, and its dominant characteristic is a relativelyhigh degree of contrast in the resulting ray picture. This inherent highdegree of contrast, while serving a most useful purpose from thestandpoint of improved radiographic quality, introduces a very definitedifficulty in the making of satisfactory diagnostic pictures, suchdifficulty residing in the inherent lack of latitude in the filmrequiring extreme accuracy in technical procedure if uniform filmdensity, quality, and tissue differentiation are to be obtained in theresulting pictures. While skilled X-ray technicians are naturally betterable to control density, quality, and differentia tion in ray picturesthan those of lesser training and experience, objectionable variation infilm density, caused by minor variations in operative procedure, almostinvariably occurs regardless of the skill of the picture makingtechnician.

Because of the wide variation in results obtained, even by highlyskilled technicians, standard radiographic procedures have been evolvedfor the making of radiographs in order to provide for at least moreuniformity in ray pictures, even though at the expense, in manyinstances, of diagnostic quality, on the theory that less harm is doneif radiographs are at least more nearly uniform in density, even thoughother procedures, affording less operational latitude, are capable ofproducing superior diagnostic pictures, in the hands of highly skilledtechnicians.

To increase the latitude of operative procedure, and at the same time toprovide for greater uniformity in over-all picture density, higher k. v.p.

wash out tissue differentiation. The present inventor, consequently, ashis primary objective, sought to provide means which would permit theuse of higher k. v. p. values, that is to say, increased ray intensityin picture making, in order to take advantage of density uniformity andthe increased latitude of the so-called higher voltage procedure,without, however, sacrificing either contrast or the ability todifferentiate tissues in the resulting picture. Contrast, within certainlimits, is essential to visibilit of detail. Every factor which has todo with maximum detail or definition should receive the greatest careand consideration, and yet, if satisfactory contrast is not obtained inthe resulting picture, the

diagnostic quality of the radiograph definitely is impaired.

-The inventor determined to ascertain why the use of increased rayintensity apparently impaired contrast in radiographs made in accordancewith high voltage procedures. A possible explanation of the phenomenonis that, perhaps, some of the diffuse radiation from the object beingpictured, under the stimulation of rays of high intensity, was able topenetrate through the lead strips or the grid, to thereby cause loss incontrast, or possibly the loss in contrast, at higher ray intensity, wasdue to other causes.

In order to obtain data for the solution of the problem, a test objectwas built, comprising a water phantom consisting of an aluminumcontainer approximately 1 millimeter in thickness, inches deep, and 14inches in diameter. Nine inches of Water in the container was employedas a scattering medium, in which was immersed a human spine, with itsmid-line 4 inches from the bottom of the container, such distanceproviding a total object-film distance of 6 inches. Five inches from thebottom of the tank, three sections of bronze wire mesh, respectively of40, 60, and 80 wires per inch, were suspended in water.

The purpose of this phantom was to provide a reasonably accuratesubstitute for the human body, inasmuch as ordinary tap water has beenfound to be similar in radiographic characteristics to fleshy bodyportions. The spine was immersed in the water for a period of 72 hoursprior to making radiographic pictures of the test object, to conditionit to approximate a live human spine. The wire mesh was used to providean added means for comparing fine detail as between grids of variousratios and at various operating k. v. p. values.

The foregoing phantom object was radiographed at various ray intensitiesand at various exposure times, using the above described grids A, B, C,D and E. All exposures were made on Eastman Blue Brand film, used inconjunction with Patterson Parspeed. intensifying screens; and allexposures were carefully processed, as; nearly as possible under thesame conditions.

The focal film distance used was 40 inches, and all of the grids wereconstructed to a 40 inch radius.

A series of pictures was made at various k. v. p. values, ranging from50 to 130, exposure time in each case being varied to compensate for thechange in k. v. p. value, as well as for changes in grid ratio, whichnecessitates a somewhat higher number of milliampere seconds to obtainuniform film density where grids of progressively higher ratio areemployed, all other factors remaining the same. The foregoing testpictures, as predicted by the inventor, revealed progressive improvementin tissue differentiating ability with increase in grid ratio, even atthe lowest k. v. p. values employed, although the improvement at minimumk. v. p. values used was barel distinguishable.

Fig. 7 is an approximate graphical representation of the relativeimprovement in picture definition experienced as a result of the presentinvention.

As noted in Fig. 7, the phantom, for comparative purposes, was alsopictured at each k. v. p. value without employing any grid whatever. Atlower k. v. p. values the improvement in picture quality of the 8 ratiogrid over the comparative pictures made, sans grid, was hardlydistinguishable over the improvement afforded in pictures made with thegrids of higer ratio. The several series of pictures made atprogressively higher k. v. p. values, however, revealed material pictureimprovement, the tissue differentiating, and consequent diagnosticpicture quality, showing astounding improvement with high grid ratiosand operating at high k. v. p. values, such improvement beingincreasingly great as a pro-, gressive function of increased grid ratioand increased k. v. p. value. At 100 k. v. p., for example, picturesmade without using a grid at all, if anything, revealed impairment indiagnostic quality over the picture made, sans grid, at the 50 k. v. p.value. The same is substantially true of pictures made with the ratio 8grid. The ratio 12 grid, however, shows a definite improvement at thehigher k. v. p. values, maximum improvement in picture quality beingattained, with a 12 ratio grid, at k. v. p. values up to values of theorder of milliamperes. The 1'7 ratio grid, likewise, affords improvementin picture quality with increase in ray intensity, maximum improvementbeing experienced at k. v. p. values up to values of the order ofmilliamperes. The 21 ratio and 34 ratio grids, likewise, show similar,butgreater improvement in picture quality with increase in k. v. p.value.

At low and intermediate k. v. p. values, pictures produced with thehigher ratio grids each afforded some improvement in picture qualityover pictures made with the next lower ratio grid, although atintermediate k. v. p. values such improvement is not extensive. At thehigher k v. p. values, however, the improvement in picture quality withincrease in grid ratio is very appreciable. 1

To verify and complement the foregoing test pictures of the phantom, anumber of pictures have been made on living human objects, Which confirmthe results indicated by the test; pictures of the phantom object.

In addition, a similar series of pictures was made of a penetrometer,comprising aluminum strips affording 11 steps, the first consisting of asingle strip of aluminum 5 millimeters in thickness, and each succeedingstep adding 3 millii'neters of aluminum. On each step of thepenetrometer, in addition to lead identifying numbers attached thereto,were placed two small squares of bronze wire mesh, respectively 40 and60 wires per inch in size. This penetrometer "Was placed in the aluminumtank of the water that could be employed, within practical limits,

Without destroying contrast between adjoining tissue portions of unlikecharacter.

As a result of all of the foregoing pictures which, aside from the highratio grids, were made with presently available radiographic equipment,it appears that, even when using grids of exceedingly high ratio, apoint of diminishing returns is reached, not only with respect to theeffect of increasing k. v. p. value using a' grid of selected ratio,but, also, in using grids of increasing ratio at a selected k. v. p.value. At a selected k. v. p. value, increasing grid ratio beyond acritical point does not result in sufiicient improvement in diagnosticquality of the resulting pictures to warrant the expense of the higherratio grid. n the other hand, in using a grid of selected ratio,increase in k. v. p. beyond an optimum value, which is different foreach grid ratio, increasing with ratio, does not result insuificient-improvement in the diagnostic quality of the resultingpictures, although there i improvement, to appear to warrant theadditional 0 expense of operating the generator at the higher k. v. p.values, with consequent reduction in generator life. It is to beconceded, however, that the foregoing observation is made in face ofresults conducted with screens, films, X-ray generators currentlyavailable, and obviously can not take into consideration futuredevelopments in- X-ray apparatus, whichcould well modify the situationinsofar as it relates to" voltages in excess of the k. v. p. values atwhich ray generators may currently be operated.

There is, of course, also the factor of mass ray absorption, that is tosay, the comparative ray absorption as between living tissue. In thisconnection, the ray absorbing capacity of alumi num, using averageprocedures, is such that approximately 9' millimeters of aluminum areequivalent to each inchof living abdominal or soft tissue. Specificmention is made of the abdominal area because the same comparison cannot be made if the tissues are, for example, those comprising the humanchest area, which is composed very largely of air spaces. Consideringfor the moment that 8 inches of abdominal tissue approximates '72millimeters of aluminum, the test. pictures, of spine and penetrometerheretofore described, indicate that the additional opacity of the spinelying within soft abdominal tissue is very small. H'eretofore, verylittle has been known about the actual difference in absorption between"the so-called spine area and the. immediately surrounding; tissues. Itnow appears, however, that the spine itself, when pictured by means of ahigh ratio grid, represents an additional opacity, in termsof aluminumthickness, of between 1 and 2 millimeters. This is an exceedingly smalldifference, for" when 2 millimeters of aluminum areimm'ersecl in 8'inches of water, the density of that. portion of the picturecorresponding with the aluminum, and the density of picture portionsrepresenting water only. is approximately the same. In view of theforegoing, there is what may be termed a very slight difference inactual opacity between various parts of the body, when comparing thespine or kidneys to the surrounding tissue, under the conditions statedabove. It would appear, consequently, that, even if all the secondary ordiffuse radiation were prevented from striking the film, there is avoltage limit, under present conditions, beyond which the ratio ofabsorption difference .between the spine and surrounding tissue is sosmall that it apparently shows as identical on the radiograph. There is,indeed, a. voltage limit, for each grid ratio, at which it is difficult,if not impossible, to determine where the spine terminates and the softsurrounding tissues begin.

Nevertheless, the efiect of increasing grid ratio above 8 is startling,to say the least, insofar as definition improvement in the resultingpicture is concerned. The higher ratio grids make possible the distinctvisualization of many areas which, in the past, have been entirelyinvisible, or, at best, barely and most indistinctly visible.

Diagnostic results obtained through use of grid ratios in excess of 8are nothing short of remarkable in comparison with what has commonlybeen accepted as the ultimate perfection in diagnostic ray pictures. Notonly are more satisfactory diagnostic results obtained on so-calledaverage patients, but a most remarkable improvement is obtained onpatients of larger than average size.

Comparable results are obtained by using high ratio grids in connectionwith the production of fluoroscopic ray pictures, particularly of partshaving thick section, such as the stomach and colon.

It is a well known fact that many users of X-ray equipment have limitedtheir work to individuals within maximum size limits. For example, it iscommon for many X-ray technicians to refrain from attempting to X-rayindividuals having a. chest thickness inexcess of 28 centimeters. Thepresent invention, however, provides means for, and method of,successfully making ray pictures of the heaviest chest structures byonly slightly increasing X-ray intensity, well within the practicalworking limits of the generator and without jeopardizing its servicelife to any great extent. The fact that greater improvement is noted in.pictures of heavier chests is certainly no handicap, particularly whenthe use of high ratio grids can also be employed to advantage forpicturing thinner patients, thereby adding much to the diagnostic valueof the re-- sulting pictures by making clearly visible details furtherout. toward the periphery of the chest,-

without, however; detracting from desirable contrast characteristics.

From. the standpoint of operative procedure, it is not necessary whenusing high ratio grids to materiallydncrease the kvp; value abovethatordinarily employed, with an 8. ratio-grid, in order to producepictures. of the. same ra-diographic density using higherratio-grids;all other; factors remaining the same. It is often possible to hold thevoltage constant, and? to change the milliamperage-secondvalue to meetincreased energy requirements; For example, tomaintain density;

if the 8 ratio grid requires- 1 second of exposuretime, the 12 ratiogrid will require seconds; the 17 ratio grid requires 15 seconds; the 21ratio gri'd requires 1.6 seconds; while the 34rati'0 The foregoing.varia l grid requires 1.75 seconds;

tions in exposure time are based on k. v. p. values within the rangebetween '75 and 100 milliamperes. At k. v. p. values below '75milliamperes, a somewhat longer relative exposure time i required forthe higher grid ratios, but not suflicient to make more than passingmention thereof. Obviously, the increase in exposure necessary at thehigher grid ratios is in no sense a deterring factor to the use thereof,being well within the operative service range of standard X-raygenerators.

The effect of increased grid ratio on tissue differentiation, inaccordance with the present invention, has made it possible to produceshadow pictures of a tissue differentiating character never heretoforeobtained by using previous or existing methods. The effect of increasedgrid ratio on detail sharpness brings forward a factor which, whileheretofore recognized in part, has received but little attention.

It is quite evident, particularly when viewing the exposures of thepenetrometer immersed in a water phantom, that, as grid ratio isincreased, the Wire mesh on the penetrometer is not only made moreplainly visible, but that the shadow pictures of the wires are sharper.This is undoubtedly due to the elimination of under cutting, which isnow established as due to secondary radiation and not to refraction.Radiation which, with a low ratio grid, will strike the film angularly,is excluded by the high ratio grid. The intervening shadows of variousstructures, thus, become increasingly sharp and clear because theradiation which is allowed to strike and affect the film more nearlyfollows along the lines of the primary beam from the ray source.Secondary, or scattered, rays, which, with low ratio grids, or, in theabsence of a grid, affect the film from various angles, are excluded sothat the true value of small focal spot size in at producing detailsharpness becomes fully efthe higher voltages required with use of highratio grids, excellent pictures of the kidneys and esoas muscles aredistinctly visible. The same procedi re for photographing lumbar spines,consequently, is now equally satisfactory for kidney radiography. In thepast, separate procedures have been essential for the photography oflumbar spines and so-called soft tissue kidney radiography procedure.

A further advantage of the present invention relates to conservation inthe life of the ray generator. Ordinarily, the recommendation of higherk. v. p. values for the operation of a generator has a tendency todecrease the life of the generator. This is especially true Where atungsten or copper deposit has formed on the inner Walls of thegenerator envelope. Such a deposit on the envelope walls is moredetrimental to generator life when operating at higher voltages. Often agenerator containing a metallic envelope wall deposits may be operatedsuccessfully at low voltage, when at high Voltage it would rapidly bedestroyed. On the other hand, if, when using high ratio grids withhigher voltages, in accordance with the present invention, accompanied ba corresponding decrease in milliampere seconds, metallic deposits onthe envelope Walls of the generator will not be as detrimental, nor willdeposits occur as rapidly, as when using comparatively low voltages atincreased milliampere-seconds. Thus, the higher voltage, lessermilliampere-seconds procedure, of the present invention, is actually infavor of longer tube life.

In this connection, it is fortunate that radiographie densit is not astraight line function when either k. v. p. value or milliampere-secondsare varied. If the relationship was such that a 29% reduction inmilliampere-seconds could only be accomplished by an increase of 20% ink. v. p., then the higher voltage procedure would very definitely affectthe tube in deleterious fashion. The present invention, however, allowsthe employment of a technique using, for example, '75 k. v. p. at 100milliampere-seconds, whereby to produce pictures with a grid of selectedratio; and increasing the k. v. p. to a value of, say, 85, orapproximately 12%, in voltage, while reducing milliampere-seconds by inmaking an equivalent picture with a higher ratio grid. Where k. v. p.has to be increased from a value of to 90, or an increase ofapproximately 30%, in voltage, the milliampere-seconds, either in theform of milliamperes, or in the form of exposure time, can be reduced by80%. Thus, in addition to the great improvement in diagnostic resultsbrought about by the utilization of higher grid ratios, in accordancewith the present invention, the wear and tear on X-ra generators is,also,

\ materially reduced.

Furthermore, fine focal spot, stationary anode tubes can be employed, asray sources, inasmuch as the focal spot size depends upon Wattage, andthis, obviously, is a multiple of kilovoltage and milliamperes. Aspreviously stated, the radiographic effect does not follow these valuesin accordance with straight line functions, with the result that it ispractical and feasible to employ very much finer, effective focal spots,safely, and still obtain superior diagnostic quality in the resultingpictures, in spite of the fact that, when using finer focal spots, ahigher voltage is employed, but at a lower milliamperage.

In radiographic procedure, both past and present, the use of cones toreduce the exposed area has been considered essential, particularly inradiography of heavy parts or relatively opaque areas, in order toimprove detail visibility. The use of cones entails accurate and precisepositioning of the tube, object and film. Ihe present invention makes itunnecessary to restrict or limit the exposed area, thereby makingentirely practical the coverage on one film only of much larger areas ina single exposure. This advantage, obviously, reduces the number ofexposures required on a generator, as well as a material reduction inthe amount of X-ray necessarily applied to the patient. By way ofexample, in accordance with current procedure, it is customary, inradiographing the spinal areas, particularly in lateral view, to maketwo or three exposures, one for the upper lumbar region, one for thelower lumbar region, including the top or head of the sacrum, and athird for the coccyx. The present invention makes possible and entirelypractical the radiography of all three areas in one ex posure, thisbeneficial result being of particular advantage in heavier than averagesubjects.

The present invention adds very materially to diagnostic results, fromevery standpoint, and makes possible the use of technical procedures is"which are far more simple and easier torempioy than any previouslyexisting technique.

It is thought that the invention and its :nu-

merous attendant advantages will be full understood from the foregoingdescription, and it is obvious that numerous changes may be made in theform, construction and arrangement of the several parts withoutdeparting from the spirit or scope of the invention, or sacrificing anyof its attendant advantages, the form herein disclosed being a preferredembodiment for the purpose of illustrating the invention.

The invention is hereby'claimed as follows: 1. The method of making raypictures, which comprises filtering picture making rays between spacedstrips of ray opaque material presented edgewise to the rays and havinga grid ratio of 'strip width, in the direction of the rays, to stripspacement, substantially in excess of 8-.

2. The method of making ray pictures, which comprises filtering picturemaking rays between spaced strips of ray opaque material presentededgewise to the rays and having a grid ratio of strip width, in thedirection of the rays, to strip spacement, substantially in excess of 8,and regulating ray intensity to obtain optimum picture definition.

3. The method of making X-ray pictures, which comprises activating anobject tobe pictured with X-rays from a generator having an anodeelectrically energized for the production of X-rays, filtering picturemaking rays between spaced strips of ray opaque material presentededgewise to the rays and having a grid ratio of strip width, in thedirection of the raysto strip spacement, substantially in excess of 8,and regulating ray intensity by adjusting the ray producing current andvoltage, at the anode of the-generator, to obtain optimumpicturedefinition.

4. A diaphragm for the screening of undesirable secondary rays in themaking of ray pictures, comprising a plurality-of spaced strips of rayopaque material, and means to maintainsaid strips in the diaphragm insubstantially equal vertical spacement betweenadjacent strips, saiddiaphragm having a grid ratio of strip width in a direction from frontto back of said diaphragm, to'strip spacement, substantially'in excessof B.

5. A diaphragm for the screening of-undesirable secondary rays in themaking of ray pictures, comprising a plurality of spaced 'strips of rayopaque material, and means to maintain said strips in the diaphragm in'substantially equal vertical spacement between adjacent strips, saiddiaphragm having a grid ratio'of strip width, in a'direction from frontto back of said diaphragm,

16 to strip spacement, substantially in excess of 8,- thev verticalspacement of said strips being of the order of 16 mils.

6., The method of making ray pictures, which comprises filtering picturemaking rays between spaced strips of ray opaque material presentededgewise to the rays and having a grid ratio of strip width, in thedirection of the rays, to strip sp'acement, in excess of 12.

7-. The method of making my pictures, which comprises filtering picturemaking rays between spaced strips of ray opaque material presentededg'ewise to the rays and having a grid ratio of strip width, in thedirection of the rays, to strip spacement, in excess of 12, andvregulating ray intensity to obtain optimum picture definition.

'8. The method of making X -ray pictures, which comprises activating'anobject to-be pictured with X-rays from a generator having an anodeelectrically energized for the production of X-rays, filtering picturemaking 'rays between spaced strips of ray opaque material presentededge,- wz'se to the'rays and having a grid ratio of strip width, in thedirection of the rays, to stri spacement, in excess of 12, andregulating ray intensity by adjusting the ray producing current andvoltage, at the anode of the generator, to obtain optimum picturedefinition.

9. A diaphragm for the screening of undesirable secondary rays in themaking of my pictures, comprising a plurality of spaced strips of may;opaque material, and means to maintain said strips in the diaphragm insubstantially equal vertical spacement-betwecn adjacent strips, saiddiaphragm having a grid ratio ofstrip width in a-direction from front toback-of said diaphragm, to strip spacement, in excess of 12.

10. A diaphragm for the screening of undesirable secondary rays in themaking of my pictures, comprising a plurality of spaced strips of rayopaque material, and means 'to maintain said strips in the diaphragm insubstantially equal vertical spacement between ady'aicent strips, saiddiaphragm having a grid ratio of stri width, in

a a direction from front to back of said diaphragm,

to strip spacement, in excess of 12, the vertical spaccment of saidstripsbeing of the order of 16' mils.

GENERAL ELECTRIC X-RAY CORPORATION, Assignee of Glenn W. FilesgDeceased, By MALVERN J. GROSS,

Vice President.

No references cited.

